Dyson DC 24 head doesn't spin?

MY Dyson DC24's head doesn't spin. The vacuum is on (brush switch is also in the on position), in the correct position, no blockage and the head brush is clean. Sometimes I can get the brush head to turn on:

1. Place the vacuum on its side so that the brush head can be removed from its housing. The vacuum is in the cleaning position, but on its side
2. Put the brush head on/off button on the off position
3. Remove the brush head from its housing
4. Put the brush head on/off button on the on position

The thing that makes the brush head spin starts spinning and this only works when the brush head is removed. If I just put the vacuum on its side the brush head doesn't move. I put the brush head back in and I can vacuum with the brush spinning but I have to do this all the time???!!!